An exhaust-aftertreatment system in a motor vehicle may include a fuel vaporizer so that fuel vapor may be provided to a downstream catalyst. Combustion of the fuel vapor at the catalyst evolves heat and removes oxygen from the exhaust stream. Either or both of these effects may allow the catalyst to reduce emissions, e.g., nitrogen oxide, more efficiently. In other examples, fuel vapor may be combusted in an exhaust-aftertreatment device in order to burn soot accumulated therein.
In U.S. Pat. No. 7,010,909, an enclosed, electrically heated glow plug is used to vaporize fuel. However, the glow plug may gradually accumulate a build-up of coke during operation. Such coking may reduce the rate at which fuel is vaporized at the glow plug, and may therefore decrease the rate of supply of fuel vapor to the catalyst.
Further, direct detection of vaporizer coking, apart from disassembling the vaporizer and inspecting the glow plug, is not provided. In the absence of direct detection, vaporizer coking can be inferred based on efficiency loss in exhaust aftertreatment, e.g. by observing greater than expected nitrogen oxide emissions from the motor vehicle. Unfortunately, this manner of detection may not specifically identify the coked vaporizer from among other possible degradation issues in the exhaust-aftertreatment system, such as degraded catalyst efficiency due to aging, for example.
The inventors herein have recognized the above issues and have devised a various approaches that may address them. Therefore, in one embodiment, a method of supplying reductant vapor to an exhaust aftertreatment device of a motor vehicle is provided. The method includes evaporating reductant on a voltage-biased, resistive heating element, the element in an enclosure configured to release reductant vapor to the exhaust-aftertreatment device, and indicating that the element is degraded if a current flowing through the element is less than a threshold current. Thus, based on the current flowing through the element, it may be possible to identify coking that degrades emission control performance. In one example, the reductant may be a fuel, such as diesel fuel. However, it may also include other reductants such as urea.
In some embodiments, the threshold current is based on the ambient temperature and/or the amount of fuel in the enclosure. Also in some embodiments, degradation may be indicated when the current flowing through the element is less than the threshold current but greater than zero, e.g., when the current is measurable but abnormally low.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.